A magnesium-manganese-based Prussian white material and its preparation method and application

Abstract

The present invention belongs to the technical field of magnesium ion batteries, and specifically relates to a magnesium-manganese-based Prussian white material and its preparation method and application. The general formula of the magnesium-manganese-based Prussian white is K n Mg x Mn y [Fe(CN)6]·zH2O has a spherical structure, an average particle size of 50nm to 150nm, a water content of 0wt% to 8wt%, a magnesium content of 0.56wt% to 20wt%, and a manganese content of 20wt% to 45wt%. This magnesium-manganese-based Prussian white material has excellent structure and performance. When used as an electrode material for magnesium-ion batteries in a 0.5MMg(TFSI)2 / AN organic electrolyte and at a current density of 100mA / g, its specific capacity reaches as high as 153mAh / g; at a current density of 1A / g, its specific capacity can still be maintained at 60mAh / g. The material also features a simple production process, low cost, and high yield, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium ion battery positive electrode materials, and in particular relates to a magnesium-manganese-based Prussian white material and a preparation method and application thereof. Background Art

[0002] In recent years, with the explosive growth of new energy vehicles and consumer electronics, the demand for lithium-ion batteries has been growing. This has led to a corresponding increase in the consumption of lithium ore and other mineral resources, such as cobalt. This has significantly limited the sustainable development of lithium-ion batteries. Therefore, there is an urgent need for a new battery that can replace lithium-ion batteries.

[0003] As a potential alternative to lithium-ion batteries, magnesium-ion batteries have the advantages of low cost, high theoretical volumetric capacity (Mg: 3833 mAh / cm 3 ;Li: 2046mAh / cm 3 ) and low toxicity. Furthermore, magnesium is naturally abundant, with its crustal reserves 300 times that of lithium (1.94% magnesium and 0.006% lithium). Furthermore, magnesium is less likely to form dendrites that pierce the separator during deposition and dissolution, which contributes to the high safety and long cycle life of magnesium-ion batteries. Therefore, magnesium-ion batteries are considered the most promising battery energy storage technology in the "post-lithium battery" era. However, magnesium-ion batteries still face a series of challenges before they can be commercialized on a large scale, and magnesium-ion battery technology still has many hurdles to overcome. For example, there is a lack of suitable cathode materials. Ideal cathode materials for magnesium-ion batteries require high reversible specific capacity and output voltage, as well as high power output. Currently, one material with great potential as a suitable magnesium-ion cathode material is Prussian white, a nanocage material with an open organic-inorganic framework structure containing cyanide ions and transition metal ions in its lattice. The structure of this nanocage material provides a good diffusion path for magnesium ions, making it a promising cathode material for magnesium-ion batteries. Manganese-based Prussian white, in particular, has a high theoretical specific capacity and high operating voltage, and holds great promise for industrialization. However, most manganese-based Prussian whites are currently synthesized in aqueous solution, resulting in a large amount of crystalline water (over 10%) in the product. During the charge and discharge process, Prussian whites containing a large amount of crystalline water can easily escape from the crystal lattice and react with magnesium salts. The presence of a large amount of crystalline water can even lead to passivation of the magnesium negative electrode, affecting the deposition and dissolution of magnesium, resulting in a decrease in battery performance. Therefore, it is necessary to develop a Prussian white material with a low crystalline water content. Summary of the Invention

[0004] To address the above problems, one of the objectives of the present invention is to provide a Prussian white material, which is a Prussian white material based on magnesium and manganese doping synthesized anhydrously. Through anhydrous synthesis, this material has a low water content (especially the content of crystal water), excellent electrochemical energy storage performance, and broad application prospects in the field of preparing inexpensive, environmentally friendly, and high-performance magnesium-ion batteries.

[0005] To achieve the above objective, the present invention can adopt the following technical solutions:

[0006] On the one hand, the present invention provides a magnesium-manganese-based Prussian white material with a general formula of K n Mg x Mn y [Fe(CN)6]·zH2O, where 0 < n ≤ 2, 0 < x ≤ 2, 0 < y ≤ 2, 0 < z ≤ 0.6. It has a spherical-like structure, the average particle size of the particles is 50 nm to 150 nm, the water content is 0 to 8 wt%, the magnesium content is 0.56 wt% to 20 wt%, and the manganese content is 20 wt% to 45 wt%.

[0007] On the other hand, the present invention provides a preparation method of the above magnesium-manganese-based Prussian white material, including: (1) By mass, 30 parts to 250 parts of divalent manganese salt, 15 parts to 80 parts of potassium ferrocyanide salt, and 60 to 350 parts of organic solvent are placed in a ball-milling device with microspheres for ball milling, washing, and drying to obtain manganese-based Prussian white; (2) By mass, 15 parts to 80 parts of manganese-based Prussian white, 15 parts to 160 parts of magnesium salt, and 50 parts to 300 parts of organic solvent are placed in the same type of ball-milling device with microspheres as in step (1) for ball milling, washing, and drying to obtain the magnesium-manganese-based Prussian white material.

[0008] On the other hand, the present invention also provides an application of the above magnesium-manganese-based Prussian white material as a positive electrode in a magnesium-ion battery.

[0009] The beneficial effects of the present invention at least include:

[0010] (1) The magnesium-manganese-based Prussian white material provided by the present invention has excellent structure and performance. When used as an electrode material for a magnesium-ion battery, in a 0.5 M Mg(TFSI)2 / AN organic electrolyte, at a current density of 100 mA / g, its specific capacity is as high as 153 mAh / g; when the current density is 1 A / g, its specific capacitance can still remain at 60 mAh / g; that is, it has excellent electrochemical energy storage performance and broad application prospects in the field of preparing inexpensive, environmentally friendly, and high-performance magnesium-ion batteries.

[0011] (2) The preparation method of the magnesium-manganese-based Prussian white material provided by the present invention is to use potassium ferrocyanide salt, magnesium salt, and divalent manganese salt as raw materials, use an organic solvent as a dispersant, and use a wet ball milling-assisted force chemical synthesis method to prepare Prussian white materials with different water contents (0-8wt%), different magnesium contents (0.56wt%-20wt%), and different manganese contents (20wt%-45wt%); the production process is simple, the cost is low, the yield is high, and it is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 : is a SEM image of the magnesium-manganese-based Prussian white material (MgMnHCF) prepared in Example 1;

[0013] Figure 2 is a SEM image of manganese-based Prussian white (MnHCF-0) prepared in Comparative Example 1;

[0014] Figure 3 is a SEM image of magnesium-based Prussian white (MgHCF-0) prepared in Comparative Example 1;

[0015] Figure 4 is the X-ray diffraction spectrum of Prussian white prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0016] Figure 5 This is the thermogravimetric analysis curve of the magnesium-manganese-based Prussian white material prepared in Example 1;

[0017] Figure 6 The charge-discharge curves of the magnesium-manganese-based Prussian white material prepared in Example 1 at different cycle numbers;

[0018] Figure 7 This is the rate performance test curve of the magnesium-manganese-based Prussian white material prepared in Example 1;

[0019] Figure 8 This is the cycle life curve of the magnesium-manganese-based Prussian white material prepared in Example 1;

[0020] Figure 9 This is a cycle life curve of the Prussian white material prepared in Comparative Example 1;

[0021] Figure 10 This is the cycle life curve of the Prussian white material prepared in Comparative Example 2.

[0022] Figure 11 1 and 2 are the first cycle charge and discharge curves of the Prussian white materials prepared in Example 1 and Comparative Example 3.

[0023] Figure 12 This is the cycle life curve of the Prussian white material prepared in Comparative Example 3. Specific Embodiments

[0024] The embodiments are provided to better illustrate the present invention, but the content of the present invention is not limited to the exemplified embodiments only. Therefore, those skilled in the art who make non-essential improvements and adjustments to the implementation solutions based on the above invention content still fall within the protection scope of the present invention.

[0025] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. Unless having significantly different meanings in the context, the expressions in singular form include the expressions in plural form. As used herein, it should be understood that terms such as "including", "having", "containing" are intended to indicate the existence of features, numbers, operations, materials or combinations. The terms of the present invention are disclosed in the specification, and are not intended to exclude the possibility that one or more other features, numbers, operations, materials or their combinations may exist or can be added. As used herein, depending on the situation, " / " can be interpreted as "and" or "or".

[0026] An embodiment of the present invention provides a magnesium-manganese-based Prussian white material, the general formula of which is K n Mg x Mn y [Fe(CN)6]·zH2O, where 0 < n ≤ 2, 0 < x ≤ 2, 0 < y ≤ 2, 0 < z ≤ 0.6, it has a spherical-like structure, the average particle size is 50 nm to 150 nm, the water content is 0 to 8 wt%, the magnesium content is 0.56 wt% to 20 wt%, and the manganese content is 20 wt% to 45 wt%.

[0027] It should be understood that the magnesium-manganese-based Prussian white material in the present invention contains, in addition to the above-mentioned water, magnesium and manganese, other conventional elements of Prussian white, such as carbon, nitrogen, potassium and iron elements.

[0028] It should be noted that it is extremely difficult to completely remove the crystal water content in the Prussian white material, and the lower the water content, the better the cycle performance of the battery. The water content of the magnesium-manganese-based Prussian white material in the present invention can be controlled below 8 wt%, and the crystal water content can be controlled below 3.12 wt%, which is much lower than the water content and crystal water content of the Prussian white material in the prior art.

[0029] Another embodiment of the present invention provides a method for preparing the above-mentioned magnesium-manganese-based Prussian white material, comprising: (1) placing 30 to 250 parts by mass of a divalent manganese salt, 15 to 80 parts by mass of potassium ferrocyanide salt, and 60 to 350 parts by mass of an organic solvent in a ball mill with microballs, ball milling the mixture, washing the mixture, and drying the mixture to obtain manganese-based Prussian white; and (2) placing 15 to 80 parts by mass of manganese-based Prussian white, 15 to 160 parts by mass of a magnesium salt, and 50 to 300 parts by mass of an organic solvent in a ball mill with microballs of the same type as in step (1), ball milling the mixture, washing the mixture, and drying the mixture to obtain a magnesium-manganese-based Prussian white material.

[0030] It should be noted that the ball milling, washing and drying in the above preparation method are all conventional operating terms in the field, and have no other specific meanings except for specific requirements for parameters. Among them, the purpose of washing is to remove impurities and unreacted raw materials. Generally, an organic solvent is selected for washing, such as anhydrous ethanol. The number of washing times can be selected according to the specific washing situation, and generally 3-4 times is selected; In addition, drying can be carried out using conventional drying methods in the field, such as using a vacuum oven for drying or a blast oven for drying; It can also be dried in stages using different drying methods, such as first using a blast oven for drying and then using a vacuum oven for drying; The drying temperature and drying time can be selected according to the specific drying situation. It is preferred to first use a 60°C blast oven for drying for 3 hours and then a 120°C vacuum oven for drying for 12 hours. Under the above drying conditions, the best drying effect can be obtained in the shortest time.

[0031] In some specific embodiments, in step (1) of the above preparation method, the microspheres are microspheres of different particle sizes in different proportions, and the particle sizes of the microspheres are 10 mm, 8 mm and 5 mm, and the ratios are 10:20:70, 20:30:50 or 5:15:80.

[0032] It should be noted that the purpose of ball milling in the present invention is to evenly disperse the raw materials, ensure more complete contact between the reaction raw materials, and promote the production of Prussian white. In the present invention, the microspheres can preferably be composed according to a ratio of microspheres of different particle sizes. More preferably, the microspheres are composed of 10 mm, 8 mm, and 5 mm microspheres in a ratio of 10:20:70, 20:30:50, or 5:15:80. At this particle size ratio, the ball milling effect is better and the prepared Prussian white has better performance.

[0033] In some specific embodiments, in step (1) of the above preparation method, the divalent manganese salt can be any one of an inorganic divalent manganese salt or an organic divalent manganese salt; and / or the potassium ferrocyanide salt can be any one or more combinations of potassium ferrocyanide or potassium ferrocyanide trihydrate. It should be noted that the above-mentioned inorganic divalent manganese salt and organic divalent manganese salt are conventional substances in the art, for example, the inorganic divalent manganese salt can be manganese carbonate, manganese sulfate or manganese nitrate; for example, the organic divalent manganese salt can be manganese acetylacetonate, manganese citrate, manganese stearate or manganese gluconate.

[0034] In some specific embodiments, in step (2) of the above preparation method, the magnesium salt is any one of an inorganic or organic magnesium salt. It should be noted that the above-mentioned inorganic magnesium salt and organic magnesium salt are conventional substances in the art, such as anhydrous magnesium chloride or magnesium acetate; similarly, the organic magnesium salt includes magnesium gluconate, magnesium hemate, magnesium citrate, magnesium oxalate or magnesium stearate.

[0035] In some specific embodiments, the organic solvent in the above preparation method can be any one or more combinations of anhydrous ethanol, acetonitrile or ethylene glycol.

[0036] It should be noted that the organic solvent in the present invention is to be able to fully dissolve the manganese salt and magnesium salt, as well as the by-product potassium salt of the reaction, so that the obtained Prussian product can be of higher purity. In the present invention, any one or more combinations of anhydrous ethanol, acetonitrile or ethylene glycol are selected for their good dissolving effect and are readily available, so any one or more combinations of anhydrous ethanol, acetonitrile or ethylene glycol are preferred.

[0037] It should also be noted that the organic solvent (including those in step (1) and step (2)) can be any organic solvent known in the art, such as any one or more combinations of anhydrous ethanol, acetonitrile, or ethylene glycol. In addition, the solvents used in step (1) and step (2) can be the same or different.

[0038] In some specific embodiments, the ball milling of the preparation method may include ball milling at 300 rpm to 500 rpm for 12 hours to 18 hours. It should be noted that the ball milling parameters of the ball milling (including step (1) and step (2)) have an impact on the prepared Prussian white. Preferably, the ball milling parameters (ball milling at 300 rpm to 500 rpm for 12 hours to 18 hours) are used. Ball milling under the above ball milling parameters has a better effect. More preferably, the above ball milling parameters are combined with the microspheres composed of the above microspheres with different particle sizes to achieve a better effect.

[0039] Another embodiment of the present invention further provides the use of the aforementioned magnesium-manganese-based Prussian white material as a positive electrode in a magnesium-ion battery. It should be noted that the aforementioned magnesium-manganese-based Prussian white material can be used as a positive electrode in a magnesium-ion battery. In a 0.5 MMg(TFSI)2 / AN organic electrolyte, at a current density of 100 mA / g, its specific capacity reaches as high as 153 mAh / g. At a current density of 1 A / g, its specific capacitance remains at 60 mAh / g, demonstrating excellent electrochemical performance.

[0040] In order to better understand the present invention, the content of the present invention is further explained below with reference to specific examples, but the content of the present invention is not limited to the following examples.

[0041] 1. Preparation of Prussian White

[0042] Example 1

[0043] (1) 80 parts of anhydrous manganese chloride and 40 parts of potassium ferrocyanide trihydrate were placed in a polytetrafluoroethylene ball mill with ZrO2 balls (ball diameter ratio of 10 mm:8 mm:5 mm = 10:20:70), and then 150 parts of anhydrous ethanol was added to the ball mill and stirred evenly. The jar was sealed and placed in a planetary QM-3SP4 ball mill at 400 rpm for 15 hours to obtain a crude product;

[0044] (2) The obtained crude product was washed 3-4 times with anhydrous ethanol to remove impurities and unreacted raw materials; the final product was dried in a 60°C forced air oven for 3 hours and in a 120°C vacuum oven for 12 hours to obtain a product of manganese-based Prussian white (MnHCF-1) with a mass of 110 parts and a yield of 91.7%;

[0045] (3) 60 parts of manganese-based Prussian white obtained in step (2), 60 parts of hydrous magnesium chloride and 180 parts of anhydrous ethanol were placed in a ball mill of the same type as in step (1) (the particle size of the ZrO2 balls was the same, and the ball mill was made of the same material and size), and ball milled at 400 rpm for 15 hours on a planetary QM-3SP4 ball mill; the obtained crude product was washed 3-4 times with anhydrous ethanol to remove impurities and unreacted raw materials; the final product was dried in a 60°C forced air oven for 3 hours and in a 120°C vacuum oven for 12 hours to obtain a final product of magnesium-manganese-based Prussian white (MgMnHCF-1) with a mass of 62 parts and a yield of 51%.

[0046] Example 2

[0047] (1) 80 parts of manganese acetate and 40 parts of potassium ferrocyanide were placed in a polytetrafluoroethylene ball mill with ZrO2 balls (ball diameter ratio of 10 mm:8 mm:5 mm = 10:20:70). 150 parts of ethylene glycol were then added to the mill and stirred evenly. The mill was sealed and placed in a planetary QM-3SP4 ball mill at 400 rpm for 15 hours.

[0048] (2) The obtained crude product was washed with ethylene glycol 3-4 times to remove impurities and unreacted raw materials; the final product was dried in a 60°C forced air oven for 3 hours and in a 120°C vacuum oven for 12 hours to obtain a product of manganese-based Prussian white (MnHCF-2) with a mass of 108 parts and a yield of 90%;

[0049] (3) 60 parts of the manganese-based Prussian white obtained in step (2), 20 parts of magnesium acetate, and 150 parts of ethylene glycol were placed in a ball mill of the same type as in step (1) (the particle size of the ZrO2 balls was the same, and the ball mill was made of the same material and size), and ball milled at 400 rpm for 15 hours on a planetary QM-3SP4 ball mill; the resulting crude product was washed 3-4 times with ethylene glycol to remove impurities and unreacted raw materials; the final product was dried in a 60°C forced air oven for 3 hours and in a 120°C vacuum oven for 12 hours to obtain a product of magnesium-manganese-based Prussian white (MgMnHCF-2) with a mass of 42 parts and a yield of 53%.

[0050] Example 3

[0051] (1) 240 parts of manganese acetate and 60 parts of potassium ferrocyanide were placed in a polytetrafluoroethylene ball mill with ZrO2 balls (ball diameter ratio of 10 mm:8 mm:5 mm = 10:20:70). 350 parts of methanol were then added to the ball mill and stirred evenly. The mill was sealed and placed in a planetary QM-3SP4 ball mill at 400 rpm for 15 hours.

[0052] (2) The obtained crude product was washed 3-4 times with methanol to remove impurities and unreacted raw materials; the final product was dried in a 60°C forced air oven for 3 hours and in a 120°C vacuum oven for 12 hours to obtain a product of manganese-based Prussian white (MnHCF-3) with a mass of 280 parts and a yield of 93.3%;

[0053] (3) 80 parts of manganese-based Prussian white obtained in step (2), 80 parts of anhydrous magnesium chloride, and 150 parts of methanol were placed in a ball mill of the same type as in step (1) (the ZrO2 balls had the same particle size, and the ball mill was made of the same material and size). The mixture was ball milled at 400 rpm for 15 hours on a planetary QM-3SP4 ball mill. The resulting crude product was washed 3-4 times with methanol to remove impurities and unreacted raw materials. The final product was dried in a forced air oven at 60°C for 3 hours and in a vacuum oven at 120°C for 12 hours to obtain 80 parts of magnesium-manganese-based Prussian white (MgMnHCF-3) with a yield of 49.5%.

[0054] Example 4

[0055] (1) 200 parts of manganese acetate and 50 parts of potassium ferrocyanide trihydrate were placed in a polytetrafluoroethylene ball mill with ZrO2 balls (ball diameter ratio of 10 mm:8 mm:5 mm = 10:20:70). 300 parts of acetonitrile were then added to the mill and stirred evenly. The mill was sealed and placed in a planetary QM-3SP4 ball mill at 400 rpm for 15 h.

[0056] (2) The obtained crude product was washed 3-4 times with acetonitrile to remove impurities and unreacted raw materials; the final product was dried in a forced air oven at 60°C for 3 hours and in a vacuum oven at 120°C for 12 hours to obtain a product of manganese-based Prussian white (MnHCF-4) with a mass of 235 parts and a yield of 94%;

[0057] (3) 80 parts of manganese-based Prussian white prepared in step (2), 80 parts of anhydrous magnesium chloride, and 150 parts of acetonitrile were placed in a ball mill of the same type as in step (1) (with the same ZrO2 ball particle size and the same ball mill material and size) and ball milled at 400 rpm for 15 hours on a planetary QM-3SP4 ball mill. The resulting crude product was washed 3-4 times with acetonitrile to remove impurities and unreacted raw materials. The final product was dried in a forced air oven at 60°C for 3 hours and in a vacuum oven at 120°C for 12 hours to obtain 91 parts of magnesium-manganese-based Prussian white (MgMnHCF-4) with a yield of 57%.

[0058] Comparative Example 1

[0059] (1) 100 parts of anhydrous manganese chloride and 30 parts of potassium ferrocyanide trihydrate were placed in a polytetrafluoroethylene ball mill with ZrO2 balls (ball diameter ratio of 10 mm:8 mm:5 mm = 10:20:70). 150 parts of anhydrous ethanol were then added to the mill and stirred evenly. The mill was sealed and placed in a planetary QM-3SP4 ball mill at 400 rpm for 15 hours.

[0060] (2) The obtained crude product was washed 3-4 times with anhydrous ethanol to remove impurities and unreacted raw materials; the final product was dried in a 60°C forced air oven for 3 hours and in a 120°C vacuum oven for 12 hours to obtain a final product of manganese-based Prussian white (MnHCF-0) with a mass of 81 parts and a yield of 62%.

[0061] Comparative Example 2

[0062] (1) 80 parts of anhydrous magnesium chloride and 40 parts of potassium ferrocyanide trihydrate were placed in a polytetrafluoroethylene ball mill with ZrO2 balls (ball diameter ratio of 10 mm:8 mm:5 mm = 10:20:70). 150 parts of anhydrous ethanol were then added to the mill and stirred evenly. The mill was sealed and placed in a planetary QM-3SP4 ball mill at 400 rpm for 15 hours.

[0063] (2) The obtained crude product was washed 3-4 times with anhydrous ethanol to remove impurities and unreacted raw materials; the final product was dried in a 60°C forced air oven for 3 hours and in a 120°C vacuum oven for 12 hours to obtain the final product, magnesium-based Prussian white (MgHCF-0), with a mass of 66 parts and a yield of 55%.

[0064] Comparative Example 3

[0065] (1) 80 parts of anhydrous manganese chloride and 40 parts of potassium ferrocyanide trihydrate were placed in a polytetrafluoroethylene ball mill with ZrO2 balls (ball diameter ratio of 10 mm:8 mm:5 mm = 10:20:70), and then 150 parts of deionized water were added to the ball mill and stirred evenly. The jar was sealed and placed in a planetary QM-3SP4 ball mill at 400 rpm for 15 hours to obtain a crude product;

[0066] (2) The obtained crude product was washed 3-4 times with anhydrous ethanol to remove impurities and unreacted raw materials; the final product was dried in a 60°C forced air oven for 3 hours and in a 120°C vacuum oven for 12 hours to obtain a product of manganese-based Prussian white (MnHCFH) with a mass of 65 parts and a yield of 54%;

[0067] (3) 60 parts of manganese-based Prussian white obtained in step (2), 60 parts of hydrous magnesium chloride and 180 parts of deionized water were placed in a ball mill of the same type as in step (1) (the particle size of the ZrO2 balls was the same, and the ball mill was made of the same material and size), and ball milled at 400 rpm for 15 hours on a planetary QM-3SP4 ball mill; the obtained crude product was washed 3-4 times with anhydrous ethanol to remove impurities and unreacted raw materials; the final product was dried in a 60°C forced air oven for 3 hours and in a 120°C vacuum oven for 12 hours to obtain a final product of magnesium-manganese-based Prussian white (MgMnHCFH), with a mass of 45 parts and a yield of 37.5%.

[0068] 2. Structure Characterization of Magnesium-Manganese-Based Prussian White

[0069] (1) SEM morphology characterization

[0070] The magnesium-manganese-based Prussian white (MgMnHCF-1) prepared in Example 1, the manganese-based Prussian white (MnHCF-0) prepared in Comparative Example 1, and the manganese-based Prussian white (MgHCF-0) prepared in Comparative Example 2 were characterized by SEM, and their SEM images are shown as follows: Figure 1 、 Figure 2 and Figure 3 As shown in the figure, compared with Comparative Example 2, the Prussian white particles in Example 1 and Comparative Example 1 are more regular, being spherical nanomaterials with a size of 20nm to 100nm. However, the particles in Comparative Example 1 are smaller, with a size of 20nm to 30nm, which leads to more serious agglomeration of the nanomaterial, which is not conducive to the insertion and extraction of magnesium ions. In Example 1, the spherical particles of the material are 50nm to 60nm in size, and secondary micron-scale channels are formed between the spherical particles, which is more conducive to the infiltration of the electrolyte, thereby greatly improving the performance of the electrode material.

[0071] In addition, the magnesium-manganese-based Prussian white prepared in other examples was characterized by SEM. The results showed that the magnesium-manganese-based Prussian white prepared in Example 2, Example 3 and Example 4 had similar properties to the magnesium-manganese-based Prussian white prepared in Example 1.

[0072] (2) X-ray diffraction characterization

[0073] The magnesium-manganese-based Prussian white (MgMnHCF-1) prepared in Example 1, the manganese-based Prussian white (MnHCF-0) prepared in Comparative Example 1, and the manganese-based Prussian white (MgHCF-0) prepared in Comparative Example 2 were characterized by X-ray diffraction. The results are as follows: Figure 4 As shown, from Figure 4It can be seen that the crystal phase structures of Example 1 and Comparative Example 1 are basically consistent, which conforms to the basic characteristics of Prussian white material. The only difference is that the embedding of magnesium ions in Example 1 replaces the positions of some manganese ions or potassium ions.

[0074] In addition, the magnesium-manganese-based Prussian white prepared in other examples was characterized by X-ray diffraction. The results showed that the magnesium-manganese-based Prussian white prepared in Example 2, Example 3 and Example 4 had similar properties to the magnesium-manganese-based Prussian white prepared in Example 1.

[0075] (3) Thermogravimetric analysis

[0076] The Prussian white prepared in Example 1 was subjected to thermogravimetric analysis. The results of the Prussian white prepared in Example 1 are as follows: Figure 5 As shown in Table 1, it can be seen that the crystal water and surface adsorbed water contents of MgMnHCF-1 are very low, namely 2.65% and 2.61% respectively. The water contents of other embodiments and comparative embodiments are also compared, as shown in Table 1.

[0077] Table 1 Water content analysis results of Examples and Comparative Examples

[0078] name Adsorbed water content (wt%) Crystallization water content (wt%) Example 1 2.61 2.65 Example 2 3.51 2.87 Example 3 2.44 2.44 Example 4 3.12 3.12 Comparative Example 1 3.58 4.33 Comparative Example 2 4.83 2.73 Comparative Example 3 5.8 12

[0079] As shown in Table 1, compared to most Prussian white materials synthesized by co-precipitation, the Prussian white material synthesized by anhydrous ball milling has extremely low crystalline water content and surface adsorbed water content, which contributes to the excellent high specific capacity and cycling stability of this electrode material in organic magnesium-ion battery systems. Comparative Example 3 shows that the Prussian white material prepared in the aqueous phase has a water content of 17.8% of the total and contains a large amount of crystalline water, which is not conducive to the charge and discharge of the Prussian white material in the battery.

[0080] (4) Characterization of component content

[0081] ICP elemental analysis was used to detect the manganese content, magnesium content, iron content and potassium content of the magnesium-manganese-based Prussian white (MgMnHCF) prepared in the example, the manganese-based Prussian white (MnHCF-0) prepared in comparative example 1, the manganese-based Prussian white (MgHCF-0) prepared in comparative example 2 and the manganese-based Prussian white (MgHCFH) prepared in comparative example 3. Combined with the results of thermogravimetric analysis, the chemical formula of the Prussian white in Example 1 was calculated to be K 0.88 Mg 0.06 Mn 1.5 [Fe(CN)6]·0.45H2O, and the results are shown in Table 2 below.

[0082] Table 2 Analysis of the main element contents of Prussian white materials in Example 1, Comparative Example 1 and Comparative Example 2

[0083]

[0084] As shown in Table 2, the manganese content in Example 1 accounts for 31.89% of the total content, and the magnesium content accounts for 0.56%. Its manganese content is lower than that of Comparative Example 1. However, the appropriate amount of magnesium intercalation helps to replenish the loss of magnesium ions, thereby exhibiting stable electrochemical performance. At the same time, compared with Comparative Example 3 prepared under experimental conditions using deionized water as the solvent, it can be found that its manganese and magnesium contents are both lower than those of Example 1. In addition, the magnesium and manganese doping in Examples 2, 3, and 4 also enables them to have good battery performance.

[0085] 3. Electrochemical performance test

[0086] In an embodiment of the present invention, the Prussian white prepared in the embodiment and the comparative embodiment is made into an electrode sheet and its electrochemical performance is tested. The method for making the electrode sheet includes: dispersing the Prussian white material, conductive carbon black and binder PVDF prepared in the above embodiment or the comparative embodiment in a mass ratio of 7:2:1 into NMP and fully grinding them to obtain a viscous slurry; then using a scraper with a thickness of 200nm to evenly scrape the slurry onto a stainless steel current collector, drying it with air at 60°C for 3h, taking it out, and then vacuum drying it at 60°C for 12h, and then cutting it into positive electrode discs with a diameter of 12mm using a cutting machine.

[0087] (1) Test of magnesium-manganese-based Prussian white prepared in Example 1

[0088] The magnesium manganese-based Prussian white (MgMnHCF-1) prepared in Example 1 was prepared into different electrode sheets according to the above-mentioned electrode sheet preparation method as the positive electrode, and a 0.5M Mg(TFSI)2 / AN organic electrolyte was used. A glass fiber separator was used as the diaphragm, and carbon cloth was used as the negative electrode. The batteries were assembled into button cells and subjected to constant current charge and discharge tests at a current density of 100 mA / g.

[0089] The charge and discharge curves of Example 1 at the 1st, 5th, 10th, 50th and 100th cycles are as follows: Figure 6 As shown, the charge-discharge specific capacity and coulombic efficiency analysis of different cycle numbers are shown in Table 3 below.

[0090] Table 3 Analysis results of charge-discharge specific capacity and coulombic efficiency of the Prussian white material prepared in Example 1 at different cycle numbers

[0091]

[0092]

[0093] Table 3 shows the charge-discharge performance of the magnesium-manganese-based Prussian white prepared in Example 1 at different cycle numbers. During the first cycle, the material exhibited a charge-discharge specific capacity of 162 mAh / g and 153 mAh / g, respectively, with a coulombic efficiency of 94.83%. As the number of cycles increased, the capacity decreased slightly, but the coulombic efficiency increased. At the 100th cycle, the charge-discharge specific capacity reached 131.4 mAh / g and 129.8 mAh / g, respectively, the coulombic efficiency increased to 98.7%, and the capacity retention rate reached 84%.

[0094] In addition, the present invention also carried out a rate test of the magnesium-manganese-based Prussian white prepared in Example 1, as shown in FIG. Figure 7 As shown, the results show that the magnesium-manganese-based Prussian white prepared in Example 1 has excellent rate performance.

[0095] (2) Test of magnesium-manganese-based Prussian white prepared in Example 2, Example 3 and Example 4

[0096] In addition, the magnesium-manganese-based Prussian white prepared in Examples 2, 3 and 4 was subjected to electrochemical performance tests according to the testing method of the magnesium-manganese-based Prussian white prepared in Example 1. The results showed that the magnesium-manganese-based Prussian white prepared in Examples 2, 3 and 4 had the same excellent electrochemical energy storage performance, high specific capacitance, good cycle characteristics and good capacity retention at high rates as the magnesium-manganese-based Prussian white electrode prepared in Example 1, as shown in Table 4.

[0097] Table 4 Performance analysis results of the batteries of Example 1, Example 2, Example 3 and Example 4 after 100 cycles

[0098]

[0099] (3) Prussian white test prepared in Comparative Example 1, Comparative Example 2 and Comparative Example 3

[0100] In addition, the first cycle charge and discharge specific capacity and first cycle coulombic efficiency of the Prussian white prepared in Comparative Example 1, Comparative Example 2 and Comparative Example 3 were tested according to the test method of Example 1. The results are shown in Table 5 below.

[0101] Table 5 Specific capacity and coulombic efficiency results of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3

[0102]

[0103]

[0104] It can be seen from Table 5 above that the first cycle charge and discharge specific capacity and the first cycle coulombic efficiency of the magnesium manganese-based Prussian white (MgMnHCF-1) prepared in Example 1 are higher than those of the Prussian white (MnHCF-0) prepared in Example 1 and the Prussian white (MgHCF-0) of Comparative Example 2.

[0105] At the same time, under the current density of 100 mA / g, the cycle life of the magnesium-manganese-based Prussian white prepared in Example 1, the Prussian white prepared in Comparative Example 1, and the Prussian white prepared in Comparative Example 2 were also compared. The results are as follows: Figure 8 、 Figure 9 and Figure 10 As shown in the results, after 100 cycles of charge and discharge, the capacity retention rates of the three were 84.3%, 81%, and 85%, respectively. This indicates that the insertion of a certain amount of magnesium is conducive to the structural stability of Prussian white, while excessive manganese doping will destroy the structure of Prussian white material, making it difficult to form large pore channels, which is not conducive to the insertion and deposition of magnesium ions. It is particularly noteworthy that the first-cycle coulombic efficiency of Comparative Example 3, which uses aqueous synthesis, is much lower than that of Example 1, and a very obvious overcharge phenomenon occurs. This is caused by the large amount of crystal water contained in the material, as shown in Table 5 and Figure 11 In addition, the cycle life test of comparative example 3 is also inferior to that of example 1 as a whole, as shown in FIG. Figure 12 Therefore, the MgMnHCF-1 Prussian white material maintains high specific capacity and high cycle stability.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be covered by the scope of the claims of the present invention.

Claims

1. A magnesium-manganese-based Prussian white material with a general formula of K n Mg x Mn y [Fe(CN)6]·zH2O, where 0 < n ≤ 2, 0 < x ≤ 2, 0 < y ≤ 2, 0 < z ≤ 0.

6. It has a spherical-like structure, with an average particle size of 50 nm to 150 nm, a water content of 0 to 8 wt%, a magnesium content of 0.56 wt% to 20 wt%, and a manganese content of 20 wt% to 45 wt%.

2. The method for preparing the magnesium-manganese-based Prussian white material according to claim 1, characterized in that: include: (1) By weight, 30 to 250 parts of divalent manganese salt, 15 to 80 parts of potassium ferrocyanide salt and 60 to 350 parts of organic solvent are placed in a ball mill with microballs, ball milled, washed and dried to obtain manganese-based Prussian white; (2) By weight, 15 to 80 parts of manganese-based Prussian white, 15 to 160 parts of magnesium salt and 50 to 300 parts of organic solvent are placed in a ball mill with microballs of the same model as in the above step (1), ball milled, washed and dried to obtain magnesium-manganese-based Prussian white material.

3. The method for preparing the magnesium-manganese-based Prussian white material according to claim 2, characterized in that: In step (1), the microspheres are composed of microspheres of different particle sizes in different proportions. The particle sizes of the microspheres are 10 mm, 8 mm and 5 mm, and the proportions are 10:20:70, 20:30:50 or 5:15:

80.

4. The method for preparing the magnesium-manganese-based Prussian white material according to claim 2 or 3, characterized in that: In step (1), the divalent manganese salt is any one of an inorganic divalent manganese salt or an organic divalent manganese salt; and / or the potassium ferrocyanide salt is any one or more combinations of potassium ferrocyanide or potassium ferrocyanide trihydrate.

5. The method for preparing the magnesium-manganese-based Prussian white material according to claim 2 or 3, characterized in that: In step (2), the magnesium salt is any one of an inorganic magnesium salt or an organic magnesium salt.

6. The method for preparing the magnesium-manganese-based Prussian white material according to claim 4, characterized in that: In step (2), the magnesium salt is any one of an inorganic magnesium salt or an organic magnesium salt.

7. The method for preparing the magnesium-manganese-based Prussian white material according to claim 2, 3 or 6, characterized in that: The organic solvent is any one or more combinations of anhydrous ethanol, acetonitrile or ethylene glycol.

8. The method for preparing the magnesium-manganese-based Prussian white material according to claim 2, 3 or 6, characterized in that: The ball milling comprises: ball milling at 300 rpm to 500 rpm for 12 h to 18 h.

9. Use of the magnesium-manganese-based Prussian white material according to claim 1 as a positive electrode in a magnesium ion battery.

Images